Fix data source grafana_user description and user_id

[pallxk]

Test terraform config

terraform {
  required_providers {
    grafana = {
      source = "grafana/grafana"
    }
  }
}

data "grafana_user" "admin" {
  login = "admin"
}

output "admin_id" {
  value = data.grafana_user.admin.user_id
}

Before

$ terraform output
admin_id = -1

After

$ terraform output
admin_id = 1

[julienduchesne]

Thanks for the fix @pallxk!